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ORIGIN OF GLACIERS. 227
(see pp. 85, 86), which have never been explored or
even reached.
Tliis glacier of Lodal presents at its lower part
decided evidences of being of great extent, though
from the valley only two or three miles of its length are
visible. It contrasts strikingly with its neighbour of
Trangedal, which is clean and white in the parts
between the blue bands and crevasses: it looks, at its
termination, like a heap of dirt, with mere streaks of
snow between. Higher up are two long black streams
of medial moraine, besides the usual lateral or shore
moraines at each side. This term "moraine," though
I have used it so frequently, may still have to some of
my readers a rather indefinite meaning, and therefore a
short explanation may be acceptable.
It must be remembered, in the first place, that, as we
ascend a mountain, the temperature decreases until wTe
reach a height where the snow that falls during the
winter does not thaw in summer. This is called the
snow-line. The height of this line varies with the
lati-tude, aspect, proximity to the sea, length of summer, &c.
Let us first of all imagine a high mountain range,
forming a single, long, smooth, sloping, rounded back,
or an angular ridge like a house-roof, and perfectly
unbroken at its sides. The snow, in this case, would
begin thawing in the spring at the lower part, and a
nearly even line would be formed by its lower boundary.
This line would rise during the advance of summer
until it reached the true snow-line, which would still
be nearly straight. At this line, then, the heat of the
Q 2
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